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Chemistry

Ksp Calculator

Convert between Ksp and molar solubility, and compare ion product Q with Ksp for precipitation.

Ksp / solubility calculator

Solubility ↔ Ksp · ion product Q vs Ksp

Solubility s = 1.3416e-5 mol/L

Molar solubility of the formula unit in pure water (no common ion).

Uses concentrations as activities and assumes the listed salt dissolves directly in pure water. Common-ion, pH, complexation, hydrolysis, and activity-coefficient effects are not included.

What is the Ksp Calculator?

The solubility product Ksp is the equilibrium constant for dissolving a sparingly soluble ionic solid. For a salt that dissolves as x cations and y anions per formula unit, Ksp = [cation]^x[anion]^y at saturation. Molar solubility s is the moles of formula unit that dissolve per liter of saturated solution in pure water.

Comparing the ion product Q (same form as Ksp but with actual concentrations) to Ksp predicts precipitation: Q > Ksp favors solid formation. The Ksp Calculator converts between s and Ksp for common salt stoichiometries and evaluates Q versus Ksp.

  • AB salt: Ksp = s²
  • AB₂ salt: Ksp = 4s³
  • A₂B salt: Ksp = 4s³
  • Q > Ksp → precipitate expected

Mathematical / chemical formulas

For MxAy(s) ⇌ x M + y A with solubility s:

Ksp = (x s)^x (y s)^y = x^x y^y s^(x+y)

s = (Ksp / (x^x y^y))^(1/(x+y))
Q = [M]^x [A]^y

Step-by-step example: Solubility of AgCl from Ksp

AgCl is type AB with Ksp = 1.8×10⁻¹⁰ at 25 °C. Find the molar solubility in pure water.

  1. Ksp = s² = 1.8×10⁻¹⁰.
  2. s = √(1.8×10⁻¹⁰) ≈ 1.34×10⁻⁵ mol/L.

Choose Ksp → solubility, salt type AB, Ksp = 1.8e-10.

Frequently asked questions

Does this include the common-ion effect?

The s ↔ Ksp modes assume pure water (no extra common ion). For common-ion problems, set up the ICE table with the extra ion and use the Equilibrium Calculator or solve algebraically; you can still check Q vs Ksp with measured ion concentrations.

Are Ksp values temperature-dependent?

Yes. Tabulated Ksp values are for a stated temperature (often 25 °C). Using a Ksp at the wrong temperature gives the wrong solubility.

References & further reading

Standards bodies, university open courseware, and peer-reviewed references that align with the methods used on this page.

Keep learning with more calculators and study guides on Online Science Tools.

Practice problems & worked examples

Practice alongside the Ksp calculator above. Each problem includes a full worked solution so you can check your reasoning step by step.

Practice problem 1

AgCl solubility

Ksp(AgCl) = 1.8×10⁻¹⁰. Find s in pure water.

Show solution

Worked solution

  1. AB salt: Ksp = s².
  2. s = √(1.8×10⁻¹⁰) ≈ 1.34×10⁻⁵ mol/L.

Answer: s ≈ 1.34×10⁻⁵ mol/L

Practice problem 2

AB₂ Ksp from s

If PbCl₂ has s = 0.016 M, estimate Ksp (AB₂).

Show solution

Worked solution

  1. Ksp = 4s³ = 4(0.016)³ ≈ 1.6×10⁻⁵.

Answer: Ksp ≈ 1.6×10⁻⁵

Practice problem 3

Precipitation check

For AgCl, Ksp = 1.8×10⁻¹⁰. If [Ag⁺] = [Cl⁻] = 1.0×10⁻⁴ M, does a precipitate form?

Show solution

Worked solution

  1. Q = (1.0×10⁻⁴)² = 1.0×10⁻⁸.
  2. Q > Ksp → precipitate expected.

Answer: Yes (Q > Ksp)

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